1. Field of the Invention
The present invention relates to a multi-point motion picture conference system in which motion pictures are communicated via communication lines between terminals respectively installed at remote points, and in particular, to a motion picture coding (encoding) and decoding apparatus to send coded motion picture information to terminals at multiple points and to receive coded motion picture information sent therefrom.
2. Description of the Related Art
FIG. 1 shows a first example of a multi-point video conference system of a conventional technology. According to features of the example, there can be used terminals for use in a one-to-one (terminal-to-terminal) motion picture communication and there is disposed a multi-point conference connecting device 106 to simultaneously establish connections for motion pictures sent from the terminals installed at many points. For example, a terminal 101a disposed at a point A for a one-to-one motion picture or video communication includes an imaging device or a video camera 102a to produce an image of an object, a coder or an encoder 103a to encode a motion picture in conformity with a characteristic of a communication line and to send the picture via the line, a decoder 104a to decode the encoded information thus received so as to restore the original image, and a display 105a to present thereon the restored image. The device 106 includes coders 109a to 109d and decoders 108a to 108d respectively as many as there are terminals disposed as above and a video (image) synthesizer 107 to establish connections between the coders 109a to 109d and the decoders 108a to 108d. Each of the decoders 108a to 108d associated with respective communication channels decodes codes or symbols sent via the channel to restore the image. The decoded image thus prepared is subjected to a synthesizing process in the synthesizer 107 and then is again encoded by the coders 109a to 109d. The coded image is thereafter transmitted to the related terminals.
FIG. 2 shows a second example of the conventional multi-point video conference system. In accordance with an aspect of the example, each of the terminals includes a plurality of decoders respectively corresponding to terminals which may possibly be specified as communication partners. With this provision, the connecting device dedicated to the conference system of FIG. 1 can be dispensed with such that coded information sent via each channel can be independently controlled. For example, a terminal 201a at a point A includes a video camera 202a to produce an image of an object, a coder 203a to encode data of a motion picture in conformity with a characteristic of a communication line and to send the encoded data via the line, decoders 204ab, 204ac, and 204ad to receive codes via related channels and to thereby restore the data of the respective motion pictures, and a display 205a to display the restored image on a screen thereof. The constituent elements conduct operations similar to those of the associated components of FIG. 1. However, this example is different from the preceding example in that the codes received via the respective channels are decoded by the decoders 204ab, 204ac, and 204ad in an independent manner, thereby displaying synthesized images.
FIG. 3 shows a third example of the multipoint video conference system of the prior art. This system has been described in the JP-A-63-276938. It is assumed that this example is configured to be operated with a packet switching network. In this system, according to the number of points connected to each other via the network, an image attained from a video camera is encoded through contraction or compression thereof and is then transmitted to a terminal. As for the configuration, description will be representatively given of a terminal 301a arranged at a point A. The terminal 301a includes a video camera 302a, a screen contraction device 303a to minimize the size of image data 309 inputted thereto, a coder 304a to encode the screen image data 309 thus compressed and to thereby produce a packet output 310a, a multiplexer 305a to receive packets 310b to 310e sent from related terminals and to produce multiplexed data in the frame unit, a decoder 306a to decode the data so as to produce a synthesized image 312 in the frame unit, and a display 307a to display the synthesized image thus decoded.
In a case where the terminal A 310a is connected to other terminals disposed respectively at the remaining four points, the the size of the input image supplied from the imaging device 302a is compressed according to a contraction scale "1/4". Namely, the size is minimized to be a quarter of the original size, thereby producing the contracted image 309. The resultant image is encoded by the coder 304a. On the receiver side, encoded data items respectively sent from the four terminals at the respective points are decoded for each frame in a time sharing manner so as to produce the synthesized image 312.
The conventional technologies are respectively attended with problems as follows.
In the first example, there is required the connecting device dedicated to the conference system. The number of connectible terminals is limited by that of the encoder-decoder pairs of the system. Moreover, with the connecting device, only one conference can be held at a time. In addition, due to repetitious encoding and decoding operations, the image quality is considerably deteriorated.
The second example necessitates a number of decoders as many as there are channels which may possibly be used to receive data. The number of connectible terminals is limited by that of the decoders. Furthermore, an equal number of terminals and decoders are required to be disposed. Consequently, for example, when the number of connected terminals is increased, the number of decoders is also increased. This remarkably increases the size of the terminal and hence the terminal resultantly becomes to be expensive.
According to the third example, the size of the presentable image is restricted by the number of connected terminals. In addition, although the image processing is accomplished in a frame unit, it is not particularly disclosed how to suppress mismatching with respect to the frame speed.
Moreover, each of the technologies above is attended with a problem that the number of connection channels is methodologically limited.